I agree that free throws are important, but its best to train free throws when you cant get a good number of prospects training. remember that free throws will train up to 14 or 15 guys and they dont have play any minutes. same for stamina. remember trainer level does not affect free throw and stamina training and both train fast. So if your training minutes get all messed up FT or ST are good options. Also as stated above, short weeks are good for training those as well. Allstar break, and end of season weeks.
You dont need to have great free thrower, but your notice a huge difference atroctious and say inept. You may not have to have more than mediocore or inept to be effective. At low level atrocious I have noticed they can barely hit a shot, even a bump to high level atrocious seemed to make a big difference. Just two training sessions in FT a season can make a big difference.